Assembly for optical to electrical power conversion

ABSTRACT

An assembly for optical to electrical power conversion including a photodiode assembly having a substrate layer and an internal side, an antireflective layer, a heterojunction buffer layer adjacent the internal side; an active area positioned adjacent the heterojunction buffer layer, a plurality of n+ electrode regions and p+ electrode regions positioned adjacent the active area, and back-contacts configured to align with the n+ and p+ electrode regions. The active area converts photons from incoming light into liberated electron hole pairs. The heterojunction buffer layer prevents electrons and holes of the liberated electron hole pairs from moving toward the substrate layer. The plurality of electrode regions are configured in an alternating pattern with gaps between each n+ and p+ electrode region. The electrode regions receive and generate electrical current from migration of the electrons and the holes, provide electrical pathways for the electrical current, and provide thermal pathways to dissipate heat.

TRANSFER. TECHNICAL FIELD

The present disclosure is related to optical to electrical powerconversion, and in particular an assembly for converting optical light,such as from a laser to electrical power.

BACKGROUND

Wireless power transfer offers an attractive solution for increasing themobility of electronic and electromechanical devices, enhancing theirusability, and increasing device design freedom, in consumerelectronics, industrial, Internet of Things (IoT) and healthcareapplications. With regard to consumer electronics, like smart phones,watches and other portable devices, near field wireless power transferoffers an intermediate solution, but falls short of more flexible,useful, and long-term solutions. For near field wireless power transfer,the wireless device to be powered includes a receiver that is generallycomprised of metal coils connected to an impedance matching network andrectifier that is used to power a load, such as a battery, and thepowering device includes a transmitter that is generally comprised ofsimilar coils to the receiver that are connected to an oscillator and apower source. When the transmitting device is supplied with a timedependent voltage and a corresponding current, the coil current isdriven to alternating high and low states in a periodic fashiongenerating a time dependent magnetic field that couples with the coilsof the receiver and allows power to be transferred from the transmittingdevice to the wireless device. Capacitive coupling between metalelectrodes based on high frequency electric fields may similarly beutilized for near field power transfer. In either case, the wirelessdevice needs to be physically close to the transmitting device, andoften times precisely aligned, which is a limiting factor to theusefulness of the technology.

Far field wireless power transfer typically relies on power beingtransferred by beams of electromagnetic radiation, such as radiofrequency and laser beams. Limiting factors associated with far fieldpower transfer include directionality, safety, and overall powertransfer efficiency. The use of laser beams to transfer power, generallyreferred to as “power beaming,” requires a direct line of sight betweena transmitter or source and the receiver or load and raises safetyconcerns because the laser radiation can cause blindness in humans andanimals exposed to low power levels for short time intervals, while highpower levels at sustained exposure periods can be deadly.

A number of possible solutions to some of the limitations of powerbeaming have been developed. In U.S. Pat. No. 6,633,026, for example,one or more light sources are generated around a single power beamforming a virtual insulator. When any one of the surrounding lightsources are interrupted, a trigger is generated that causes the powerbeam to be turned off. This system relies on a receiver that isphysically separate from the wireless device and largely stationary asthe system, in this patent, lacks the ability to track mobile electronicand electromechanical devices. The system also relies on a two-partprocess to switch the power beam on, with a first light source searchingfor receivers needing power at previously known locations and the powerbeam and virtual insulators then being turned on once the receiver hasbeen located. U.S. Pat. No. 7,068,991 describes a complicated powertransfer system, which includes either microwave or laser beams, to bothtransfer power and provide data communication, but neglects to describein any technical detail, the process by which power is transferred. Aswith U.S. Pat. No. 6,633,026, the system described in U.S. Pat. No.7,068,991 relies on the transmitter sending a preemptive power requestsignal to the receiver, which results in wasted power when no devices oronly fully charged devices are within range of the transmitter.

U.S. Pat. No. 7,423,767 describes a different approach that relies onmechanical beam steering to align the receiver with the incoming powersignal, but this introduces a host of shortcomings related to mechanicalaspects of the system. Device localization and tracking are notdescribed in sufficient detail for one skilled in the art to implementthe invention in a physical system. The patent only describes detectingthe receiver based on a reflection from the receiver, which in turnrequires locating the center point of a reflective ring and comparingreflected light from each of a number of mapped points. As thetransmitter beam approaches the center of the ring reflector, itimpinges upon the photovoltaic device from which reflections willdecrease significantly. Likewise, as the transmitter beam radially stepsaway from the center of the ring, it misses the target. The reflectionswill decrease significantly. There is no explanation on how these twostates are differentiated. Likewise, U.S. Published Application No.US2010/0012819 describes a transmitting laser and lens that are attachedto a pointing mechanism. The described beam steering solution requires acamera to locate the optical to electrical converter, such as aphotodiode, of the receiver with enough precision to direct a beam with<10 mm spot size towards it. In practical terms, this creates asignificant size constraint on the optical elements of the wirelessdevice and puts all of the safety responsibility on the transmitter, forwhich there is no tolerance to faults in the transmitter, whereas safetyis handled by both transmitter and receiver in the invention describedherein. U.S. Pat. No. 5,229,593 describes a stationary transmitter andreceiver that operates at safe levels when the power beam is not beingreceived by the receiver and unsafe level when it is being received. Thelimitation for mobility of the transmitter and receiver better suitspermanent structures or terminals, such as broadcast towers orcommunication stations, rather than consumer electronics or mobileelectromechanical systems.

A critical element of far field power transfer systems is the receiver,and a key aspect of the receiver is the manner in which light energy istransduced into electrical energy. One existing solution to optimizingelectrical transduction is to increase the size of the photosensitiveregion of a photonic sensor. This, however, requires more physical spaceon the receiver side, which reduces the utility and increases the costof the device. Photovoltaic cells, such as solar arrays have become muchmore efficient at converting photons to electrons, but are generallyoptimized for visible light and require a significant amount of physicalspace, e.g., the average size of solar panels used in rooftopinstallations is 65 inches×39 inches with the individual photovoltaiccells measuring 6 inches×6 inches. Integrating spheres, which are hollowvolumes having small entrance and exit ports reflect incident light offof internal surfaces into an optoelectronic device that converts thelight into energy. Such spheres tend to be less efficient and alsorequire more physical space and thus are generally too large to beuseful for mobile devices and many other applications. Thermopilesrequire less physical space and can operate over large bandwidths, butare inefficient as they convert the light energy to heat, which is thenconverted to electrical energy. Many sensors that operate inphotovoltaic mode implement contact arrangements that obscure incidentlight on photosensitive regions (by virtue of their electricalconnections), thereby yielding lower coupling efficiency. Similardevices are constructed without material composition or geometricarrangement that is specifically designed for single mode light, thatcan be emitted from a laser.

SUMMARY

An assembly for optical to electrical power conversion is disclosed. Theassembly comprises a photodiode assembly that includes a substrate layerhaving a light exposed side and an internal side, an antireflective anantireflective layer adjacent the light exposed side, a heterojunctionbuffer layer positioned adjacent the internal side; an active areapositioned adjacent the heterojunction buffer layer, a plurality of n+electrode regions and p+ electrode regions positioned adjacent theactive area, and back-contacts configured to align with the electroderegions. The antireflective layer may be configured to prevent incominglight from reflecting off of a surface of the light exposed side. Theactive area may be configured to convert photons from the incoming lightinto liberated electron hole pairs. The heterojunction buffer layer maybe configured to prevent electrons and holes of the liberated electronhole pairs from moving toward the substrate layer. The plurality ofelectrode regions may be configured in an alternating pattern with gapsbetween each n+ electrode region and each p+ electrode region and may befurther configured to receive and generate electrical current frommigration of the electrons and the holes, to provide electrical pathwaysfor the electrical current and to provide thermal pathways. Thealternating pattern may include a series of pie shaped sections witheach pie shaped section having a narrow end adjacent a central area ofthe n+ electrode regions and the p+ electrode regions, and each pieshaped section may be formed of interleaved rows of the n+ electroderegions and rows of the p+ electrode regions. An anode back-contact mayalign with a portion of the alternating pattern corresponding to therows of the n+ electrode regions and a cathode back-contact may alignwith a portion of the alternating pattern corresponding to the rows ofthe p+ electrode regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a transmitter in accordance withan embodiment;

FIG. 2 is an illustration of a transmitter enclosure in accordance withan embodiment;

FIG. 3 is a block diagram illustrating a receiver in accordance with anembodiment;

FIG. 4A is an illustration of a compound parabolic concentrator mirrorof the receiver in accordance with an embodiment;

FIG. 4B is an illustration of a compound parabolic concentrator mirrorwith a tapered inlet of the receiver in accordance with anotherembodiment;

FIG. 5 is a cross-sectional view of the photodiode assembly of thereceiver in accordance with an embodiment;

FIG. 6 illustrates the penetration depth of light as a function of itswavelength;

FIG. 7 is a cross-sectional view further illustrating a portion of thephotodiode assembly of FIG. 5 to better illustrate the light absorptionand electron conversion capabilities of the photodiode assembly inaccordance with an embodiment;

FIG. 8 is a cross-sectional view further illustrating the PIN structureof the photodiode assembly of FIG. 5 and the carrier transport mechanismin accordance with an embodiment;

FIG. 9A illustrates a top view of the back-contact pattern of thephotodiode assembly of FIG. 5 in accordance with an embodiment;

FIG. 9B illustrates a top view of the back-contact pattern of thephotodiode assembly of FIG. 5 in accordance with another embodiment;

FIG. 10 illustrates a cross-sectional view of the photodiode assembly ofFIG. 5 with the back-contact pattern illustrated in FIG. 9 integratedinto a printed circuit board (PCB) configuration in accordance with anembodiment;

FIG. 11 is a top view of the PCB configuration of FIG. 10;

FIG. 12 is a cross-sectional illustration of light interaction between aFresnel lens and a photodiode array in accordance with an embodiment;and

FIG. 13 is an illustration of a lens stack in accordance with anembodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The wireless power transfer system of the present disclosure may becomprised of two core elements, the transmitter and the receiver, whichenable the efficient transmission of power wirelessly from thetransmitter to a single receiver or multiple receivers simultaneously,using a collimated infrared laser beam. The transmitter may bestationary, connected to a reliable power source, moderately costsensitive, and moderately space constrained. The receiver may be mobile,contain a battery or capacitive power source (from which power can beboth sourced and sunk, i.e., output and input), cost sensitive, and veryspace constrained.

From an operational perspective, the transmitter may be responsible forsensing the environment, detecting the presence of suitable receivers,and participating in bidirectional communications with those receiversto determine the precise location of their optical elements. During thisinitial device localization, a safety system is implemented and thenmaintained in constant operation during nominal functionality, asfurther described below. The transmitter may also control thetransmission of an infrared (IR) laser power beam and the opticsassociated with delivering power to the receiver's optical elements in amanner that meets regulatory safety requirements. In order to maintainsystem safety, the transmitter may strive to cut off the high-powerlaser beam in as short a time as possible when the safety system detectsan interruption, does not receive expected information, the power beamis misaligned, or a receiver's location is lost. The transmitter mayalso receive, process, store, and forward data about any connectedreceivers to a centralized digital database.

The receiver may be responsible for broadcasting its presence to theenvironment and bidirectionally communicating with the transmitter. Thetransmitter may be responsible for coordinating the priority of wirelesspower transfer based on a credential exchange with each of a number ofpotential receivers and may rank the priority of each receiver in orderto establish the order in which each receiver is charged. The preferencefor priority may be established by the user/owner of the wireless powertransfer system or be pre-scheduled in the same manner or be left to astate determined by factory settings. The receiver may also cooperatewith the transmitter in order to determine the precise localization ofthe receiver's optical elements. Once the receiver is in or hasestablished communication with the transmitter, it may continuouslytransfer power and charging state information to the transmitter.

Given specific power and timing limitations involved with the safewireless transmission of power, the receiver may also communicate devicespecific information back to the transmitter (i.e., sensor data could bepassed over the free space optical communication (FSOC) link to thetransmitter, given appropriate overhead in the wireless powertransmission). Similarly, the transmitter may communicate commands ordata over the FSOC link to the receiver given appropriate overhead inthe wireless power transmission. The transmitter may also transmit, viaa wireless or wired connection, system or device specific information ordiagnostics to a cloud or connected database. Hence, the transmitter andreceiver may establish a bidirectional data communication channelenabling the transfer of data unrelated to the power operation orlocation of the device itself. Various IoT or other similar devicescould both receive power and other data and/or commands through thewireless power transfer system. For example, a smart thermostat couldsend room temperature information to the wireless power transfer system,which could then transfer that temperature information to an HVACcontroller or an automated window shade that is also powered through thewireless power transfer system.

An illustration of the transmitter in accordance with one embodiment isshown in FIG. 1. As illustrated, the transmitter 10 may include a powersource 12, a laser system 14 for generating one or more power beams andone or more light beams, optomechanics 16 for beam steering, a processor18 and associated power control logic 19 for controlling the lasersystem 14 and optomechanics 16, as well as a communication subsystem andsafety subsystem. The transmitter 10 may perform all of the majorcompute processes required to keep the system accurate and safe. At thelogic level, the processor 18, such as an ARM Cortex processor, mayprovide high-level control over the majority of functions for which thetransmitter is responsible. The processor may contain command setsspecific to various transmitter functions such as beam steering, powerbeam output control, FSOC data processing, thermal control, sensor datatransfer, sensor fusion, and system reporting. An additionalhousekeeping integrated circuit (IC) 11 may be utilized to provide overand under current protection/monitoring of the DC to DCconverter/regulator 15 and overall fault management, reporting andclearing. This may be particularly useful when the wireless powertransfer system is utilized medical, aerospace and other higher riskenvironments when there is a greater need to maintain a safe state ofthe system regardless of various faults that may occur, thereby creatinga fault-tolerant system that is generally required by governmentalregulations for devices used in these applications.

Power for the transmitter 10 is derived in this embodiment from a stablepower source 12 coupled to a laser AC/DC power supply 20 through a powerline filter and ESD protection circuitry 13. The power source 12 maycome in many forms, such as a high voltage battery, a wall outlet orother secondary power generator off the main power grid. The inputsignal may be AC from 120Vac to 240Vac and may be plugged into astandard wall outlet (15 A/20 A for North America, 16 A+ for EU) or astandard DC voltage at an amplitude commensurate with systemrequirements. The input power 12 may pass through the power supply 20that may include a 2-stage converter that converts the AC voltage to DCvoltage, that is unregulated or regulated, and then a DC to DCconverter/regulator 15 to regulate the output into a plurality ofvoltages. From there, the voltage may be down converted as necessary tosupply various sub circuits.

In this embodiment, three power busses may be included, such as a laserbus for biasing laser components, a logic bus for biasing processing andcompute components, and a motor bus for biasing electromechanical loadsor subsystems. Each subsystem of the transmitter 10 may derive powerfrom one of these three busses. To isolate noise, the power busses maybe decoupled from one another via passive components, split grounds, oron-board shielding (e.g., egg crating). The logic bus may be providedthrough the complex programmable logic device (CPLD) 22. As thoseskilled in the art may realize, different bus and/or power distributionmethods may be used depending on the components and converters used.

The power supply 20 for the laser diode of the laser system 14 may be ahighly regulated (stabilized) current supply that operates in currentcontrol mode. The supplied current may be monitored against a currentset point to generate an error value. That error value may be fed backinto the power supply logic and/or controller/laser diode driver 17 tofine tune the output. The power supply 20 and/or laser diode driver 17coupled to the power supply 20 may also incorporate a command inputassociated with an output from the CPLD 22 of the safety system, whichmay serve to disable the power supply 20 and/or the laser diode driver17 should an obstacle in either partial or full obstruction the path ofthe light beams be detected or for other safety reasons. In order toshut off the power or driver quickly, the bandwidth of the power supplymay be greater than 5 kHz. The laser source 24 may be, but not limitedto, a laser diode on a C-Mount/TO-Can/integrated module package and maybe fixed in place. So that the transmitter can accommodate multiplereceivers, a number (n) of identical laser diode sources 24 may be fedfrom the same power supply 20 or by separate power supplies for eachlaser diode. A heat sink with or without an active cooling device may beincluded to temperature regulate the power supply, regulator and drivercomponents.

In an embodiment, the output of the laser source 24 may be split by beamsplitters, optical filters, or mirrors into two or more separate beampaths. The resulting beams may be used in separate power beam channelsto supply two or more devices from a single source. In an embodiment inwhich a single source may supply multiple receivers, a series of activeoptics may be used to decrease optical output power for a single channelin the event that one receiver is blocked and the other is not, therebyeliminating the need to turn off the single laser source to both devicesin the event that a block occurs with one device.

In addition to the power beams being identically fed from the laser bus,a different, lower power beam may also be supplied by one or more FSOClasers. The FSOC channels may be established with a single or multiplelight emitting diodes (LEDs) or low power laser diodes to transmitoptical data and single or multiple photodiodes to receive optical data.FSOC components may be configured to operate off either the laser orlogic bus depending on subsystem voltage requirements and efficiencies.The transmitter and receiver may be made modular by implementingidentical FSOC components, wherein the transmit device from thetransmitter communicates with the receive device in the receiveridentically to the transmit device in the receiver to the receive devicein the transmitter.

The logic bus may provide a reference voltage for all of the componentscontrolling logic functions. This may include the CPLD (safety) 22 (suchas XILINX or Intel CPLDs, the processor 18 (such as Intel andFreescale), the microcontroller unit (MCU) 26 (such as an ARM Cortex orsimilar products by XILINX, or NVIDIA), a camera 28, auxiliary sensorsor secondary power regenerators, and finally any active opticalapplications needed for future device capabilities (such as variablebeam splitters/attenuators, polarization plates, etc.).

The motor bus may be responsible for supplying appropriate voltage tothe two-axis beam steering brushless DC (BLDC) motors 30 as theprinciple optomechanical components 16. Two-axis motors 30 may includereflective or refractive optics and be employed to enable the projectedlight to provide a wide cone of coverage extending from the opticalinterface of the transmitter housing 32 (as further illustrated in FIG.2) to the walls and/or floors of the room or location in which it isstaged. Control of the motors 30, augmented by a feedback loop, isprovided by a motor controller 31, which is a logic driven component ofthe MCU processor 26. Alternative methods for beam steering, such asMEMS mirrors, gimbal assemblies, Risley prisms, liquid crystalwaveguides, optical phased arrays, or other solid-state beam steeringassemblies may be used that are familiar to those skilled in the art andare not precluded from this disclosure.

As noted above, the processor 18 provides most of the logic control ofthe transmitter, including partial FSOC photodiode 27 and camera 28monitoring, FSOC LED 25 command, and beam steering logic command of theoptomechanical system 16. Communicative coupling between the FSOC LED 25and FSOC photodiode 27 may be provided by IR transceiver 29, which iscoupled to the processor 18, and includes an encoder/decoder. Theseparate MCU processor 26 may feed auxiliary input to the optomechanicalsystem 16 to better assist with beam steering accuracy and thermalrequirements, including but not limited to: command of a fan or athermal electric generator (TEG) 33 or cooler based on thermal readingsfrom a thermocouple or temperature sensors (not shown), fine beamsteering adjustments based on accelerometer 34 feedback, position orconfiguration modification based on requirements for potential futureactive optics (not shown). Power management of the TEG 33 may beprovided by step-up transformer 35.

Closed loop control of the FSOC LED 25, assisted with direct receiverdistance detection, may be provided via a computer vision-basedalgorithm that determines the needed strength of the FSOC LED transmitsignal based on the pre-calibrated lighting conditions of the room orlocation as detected by camera 28 and processed by processor 18. Inother words, if the disclosed wireless power transfer system is utilizedin a room or location with significant ambient or shifting naturallight, it may be desirable to utilize pictures taken by the camera 28 toadjust, i.e., increase, the output power of the FSOC LED 25. If thelighting in the room or location was below the pre-calibrated lightingconditions, then the output power of the FSOC LED 25 may be decreased.By adjusting the amount of output power needed based on feedbacklighting conditions of the operational environment, transmissionefficiencies may be realized.

The CPLD 22, which may be a separate IC or which may have itsfunctionality integrated into a more complex IC, or a dedicatedsafety/control component, may be responsible for the overall command andcontrol of the safety subsystem. This may include shutdown commands tothe laser diode power supply 20, the processing of optical power levelsfrom a monitor photodiode or optoelectronic sensor (not shown), thegeneration of any error or fault messages to the processor 18, and anyother actions associated with maintaining user safety as a result ofimpingement of the high-powered laser beam. The CPLD 22 may require thepresence of two signals from: 1) the additional processor 26 and 2) themain processor 18 in order to enable the laser source 24 to reachoptimal power beaming levels. Additional electrical components (mostlynot shown) may include passive devices responsible for filtering,grounding, shielding and the like, converting power, transmittingtelemetry over WiFi, Bluetooth, or dedicated RF link, sensors requiredfor initial calibration, additional indicator LED or screens providedfor the benefit of the user but not required for system functionality,etc.

The optical and optomechanical components of the transmitter 10 mayshape and control laser beam properties in two axes. A first set ofcollimating optics 40 are positioned off the edge facet of the laserdiode 24. The collimating optics 40 may be a molded set of n lensesresponsible for producing a beam parallel in two axes for injection intothe beam steering assembly. The collimating optics 40 may include a FastAxis Collimator (FAC) and a slow axis lens to shape the beam(s) in twodimensions. The FAC may be comprised of an aspheric cylinder ofappropriate diameter and thickness, a ball lens, a small section offiber optic cable, or a plurality of optics used in conjunction orindependently. A small truncated section of appropriate fiber opticcable may be used as a cheap and quick lens for fast axis collimation.In one embodiment, a section of fiber optic cable, slightly longer thanthe longer dimension of the laser facet may be secured by mechanicalmeans to the front face of this facet such that the long axis isparallel and adjacent to the long axis of the facet. The fiber opticcable will act in a similar manner to an aspheric cylindrical lens byparallelizing all divergent rays from the laser or slight source. Thismethod may provide a quicker way to achieve collimation than use ofdelicate and often expensive fast axis lenses.

The laser diode 24 may be uniquely designed to produce light with asingle polarization by uniquely shaping or growing the laser cavityregion. Since reflections off the receiver surface are a concern for anyhigh-power free space optical system, ensuring that the generated lightis p polarized may help to reduce reflections, even past 60 degrees beamangle of incidence. This may be achieved through the addition of thep-polarized waveplate 42 that is placed over a corresponding collimatingoptics 40 (i.e., there may be n waveplates 42, which corresponds to acollimating optics 40 and a laser source 24). A spatial filter withV-coating may also be added to ensure uniform profile of the outputbeam(s).

In an embodiment, the remaining optics may be part of the optomechanics16. The optomechanics 16 may include a beam steering assembly 44 havinga 2-axis galvanometer mirrors that is driven by rotary BLDC motors 30.The galvanometer motor control is coordinated by the MCU 18, withcommand to the motors 30 based on interpreted feedback from the FSOCphotodiode 27. The structure of the optomechanics 16 is modular, meaningthe optomechanic 16 structure may be substituted in and out of differentpackages and therefore can be used in a plurality of devices, housingsand enclosures. The mirrors of the optomechanics 16 may be thin film,multi-layer silver and or gold coated for best response in the IRwavelength range and environmental survivability. The mirrors may rotatedepending on motor 30 position, deflecting the beam toward the receiver.A final set of output optics, outlet lens assembly 46 may be included toactively focus the power beam. Limiting beaming distances for thissystem in a range of up to 50 feet may eliminate the need for dynamicfocusing, but the current disclosure is not limited to this particularlydistance and may be used for longer free space optical applications.Long-wave pass filters (not shown) may also be used on potential lensesin front of FSOC optoelectronics, including IR camera 28, FSOCphotodiode 27 and FSOC LED 25. Ideally, these filter additions are notnecessary, but are noted here for completeness.

The transmitter enclosure 32, which is further illustrated in FIG. 2,may be a standalone structure or incorporated into other devices, suchas but not limited to: light fixtures, smoke detectors, securitycameras, drones, and other mobile or static systems, depending on thenature and location of its use. The physical structure 32 may house allof the components of the transmitter 10. The mechanical structure may bedesigned to satisfy the performance and environmental requirements of awireless power beaming system. The structure may incorporate mechanicalfeatures and specific materials to increase conventional convective andradiative thermal dissipation for the power beaming laser diode 24and/or other high current loads. Mechanical isolators may be utilized tostabilize the system from inherent vibrational resonance associated withhuman movement across rooms of various constructions as well asmechanical system influences, such as HVAC systems and the like. In anembodiment, the portion of the enclosure 32 where any optical beampasses may be made of a material that is opaque at visible wavelengthsand transparent in the near infrared wavelength range. The entireenclosure 32 may also be made of this material. In that manner, a userwill only see an enclosure, like the outside of a fire detector on aceiling, and not the active/internal components. The materials andoverall mechanical structure may allow it to be used in a plurality ofenvironments.

As the power beam is transmitted in a form that can be dangerous tohumans and animals, safety aspects of the system are of criticalimportance. Embodiments of the present disclosure therefore include abuilt-in safety system to prevent human, animal and obstacle exposure tolaser radiation in excess of eye safe levels, which trigger the mostrestrictive levels of safety regulation. In accordance with the presentdisclosure, the system is inherently safe, which is defined as followswith reference to the architecture of the system. A bidirectional lowpower laser beam, or FSOC channel, is established between a transmitterand one or more remote receivers, one or both of which may be mobile.The channel laser power is below Maximum Permissible Exposure (MPE)limits and is therefore classified as eye safe and can therefore beoperational at all times without fear of adverse effects on intersectingobjects. The channel substantially co-propagates with the high-powerlaser beam such that they are not more than 1-10 mm apart forsubstantially an entire distance from the optical interface of thetransmitter to the receiver. Due to their close proximity, the low powerlaser beam is interrupted before the high-power laser beam can beinterrupted and interruption of the low power laser beam results in thehigh-power beam laser being shut down. As is known, laser radiation canbe used for communication when there is a well-established Line of Sight(LOS) between the transmitter and receiver. In one embodiment, in theevent that this LOS is broken for any number of obstacles or situations,the high-powered laser is designed to terminate within the timerequirement allowable for observance of maximum permissible exposure(MPE) limits congruent with Accessible Emissions Limits (AEL). For ClassI, eye safe classification, AEL is equivalent to MPE. Because LOS isbuilt into the safety features and overall functionality of the system,one cannot exist without the other; hence, the system can be classifiedas “inherently safe.”

In one embodiment, the hardware and software implementations of thesafety system may consist of a transmitting source, usually oneconnected to a reliable and stable power source, and a mobile orperipheral receiver, containing minimal electrical parts andimplementing basic Digital Signal Processing (DSP), and coupled with thehost device in which it is integrated. This embodiment of the safetysystem may be designed explicitly for high power laser beaming in theNear IR (NIR) wavelength regime. The timing of the system may be easilyadjusted to accommodate scaling safety requirements associated withvisible or even UV light. The premise of the system in this embodimentmay rely on fast and accurate detection of obstacles within the beampath that couple dependency of system latency with maximum permissibleexposure (MPE) levels. As further described below, additionalembodiments of the safety system include hardware and softwareimplementations that will shut the high-power laser beam down for otherreasons.

For background purposes, the current governing standard for laser safetyand laser safety certification of consumer sold products are 21 Code ofFederal Regulations (CFR) Part 1040 entitled “Performance standards forlight emitting products in the United States,” and IEC60825-1, thelatter of which regulates the safety of laser products in Europe and therest of the world. In 2007, the FDA issued Laser Notice 50 thatdescribes the conditions under which equipment manufacturers mayintroduce into U.S. commerce laser products that comply with theIEC60825-1 standard. This document effectively harmonized thecertification standards for Europe and the U.S. to provide a “leastburdensome approach.” Laser Notice 50, with reference to IEC60825-1,established all system latency and detection mechanisms responsible forbeam operational safety. The popular ANSI Z136.1 documentation alsoprovides a guideline for classifying such lasers and safety/controlmeasures associated with their safe operation, but does not apply as acertification standard against which products seeking said certificationshould be compared. Naturally, these standards are subject to change.

In typical certification governance, laser products are discretized intoclasses by virtue of their output characteristics. Depending on pulsedor continuous wave (constant or CW) output either a Watt or Joule (Wattseconds) limit level is, generally, applied. Accessible emissions limitsor (AEL) are determined as a product of the MPE multiplied by an areafactor, referred to as the limiting aperture.

With regard to the present disclosure, operation of the laser source maybe CW or pulsed. In CW operation, the average power delivery is oftenfar higher than that of a pulsed system. Although a CW system isdescribed below for ease of disclosure, a pulsed system of various pulselengths could also, be used. This configuration may also be implementedfor a receiver device (with a lower power rating) in operation with atransmitter, without dynamic power control. In an embodiment, atransmitter device emits a high-powered CW light. At the same time,either co-propagated and in parallel with the high-power beam, aneighboring low power laser beam may also be emitted from a differentelectrical to optical component, but positioned within millimeterproximity to the high-powered source. The lower power laser beam mayhave far greater divergence than the high-power beam and thus divergeover a shorter distance that the high-power beam. For purposes of thepresent disclosure, the operational or working distance of this systemmay be within the range of 1 foot to 30+ feet. This operational distanceenables the lower power photodiode assembly of the receiver to havegreater tolerance on placement, but higher requirement on sensitivity.The co-propagated low power laser beam thereby creates a virtualenclosure around the higher power beam over the operational distance. Ifthe system is used over distances such as those specified above,atmospheric absorption and scattering may not cause an issue.

In order to increase usefulness and capability of the system, a digitaldata stream may be modulated onto the low power laser beam. Modulationschemes come in various forms and complexities. In order to createefficient systems, there may be a large reliance on low overhead powerconsumption, or in other words keeping the power used by all other partsof the safety system as low as possible. The modulation scheme istherefore carefully chosen to balance:

-   -   1. Power consumption overheard, which includes processing, data        storage, A/D or D/A conversion, and transmission;    -   2. Serial data rate, which is the rate at which the system can        adequately communicate receiver information and the transmitter        can interpret said information in order to follow an appropriate        action/command;    -   3. Part count/type, i.e., decreasing the part count, especially        on the mobile receiver side, decreases the footprint and space        needed for implementation of such subsystems.    -   4. Multiple access, or the ability to accommodate multiple        mobile receivers with a single transmitter.

The transmitter/receiver system may have coupled modulation/demodulationarchitectures that associate unique frequencies, timing, or signalqualities to coupled devices. In this embodiment, it is possible tosupport numerous receiver devices with a single transmitterdifferentiated by their serial data rate, pulse amplitude, or timing oftransmission. This may be similar to how the NTIA Office of SpectrumManagement or FCC manages spectrum usage, i.e., the transmitter managesdevice wavelength usage. OFDM, OCDMA, or M-PPM are also acceptablemodulation methods and are not excluded from the present disclosure.

In its simplest form, modulating the low power laser beam by turning iton and off (On/Off Keying—OOK) can be used to convey a series of bits,or a bit sequence and is considered a common communication protocol inIntensity Modulated/Direct Detection (IM/DD) schemes. A bit sequencelibrary known to both the transmitter and coupled receiver providemeaning to the alternating bit sequences. OOK keeps processing overheadrequirements low and increases the effective bandwidth of the system,which increases the speed of signaling and therefore decreases latency(up to the point where processing bottlenecks are due to thehardware/chip speeds). OOK is one such modulation scheme that may beused as full or partial satisfaction of communication and safetyrequirements. It should be apparent to those skilled in the art thatother modulation schemes can be effectively used to achieve similarpurposes.

The MPE/AEL levels may be designed such that the shorter the exposurethe higher the allowed optical power to meet the same energy exposurelevels for pulsed operation. In essence, obstacle exposure to the beammay be considered a pulsed exposure, even though the system is operatingwith a CW output, considering the cut-off time achievable by thetransmitter. At the upper wavelength range of the IR-A and all of theIR-B wavelengths, the radiation is generally considered eye safe due tothe long wavelength, i.e., the eye does not focus the radiation to theretina nor does the radiation penetrate to lower levels of theepidermis. Cornea exposure to laser radiation is hazardous for spotheating and the same is true with other soft tissue at thesewavelengths. Spot heating requires the application of a high-power lasersource of significant power across a small surface area for a specifiedduration of time. Thus, hazardous conditions for this system aretemporal. Some embodiments of the present disclosure seek to satisfysuch timing requirements.

If the disclosed system is deployed in environments that are considereduncontrolled, one in which occupants are nominally unaware of exposureto laser radiation, safety is a requirement for lasers above the class 1level. In such situations, laser radiation hazards are dependent on thetime of exposure, the radiation power level, and the wavelength of laserradiation. In an embodiment, the power beam laser wavelength may bechosen based on a number of factors. One such factor may be thewavelength range in which radiation is least hazardous to unaware users.In such instances, the wavelengths of the laser that are not focused tothe retina have higher exposure limits and are therefore preferable forthe embodiment.

The transmitter architecture, in effect, acts as a watchdog for thereceiver circuit. If a predetermined time period passes during which thetransmitter does not receive data from the receiver or a lack of bitsare counted from the receiver or a specific bit sequence is transmittedfrom the receiver, the transmitter associates this absence/bit sequencewith a specific message and shuts the laser diode off or decreases theoutput to Class 1 levels. By providing constant feedback between thereceiver and the transmitter, the system is functionally capable ofsafety, as well as receiver tracking. In addition to the receiverfeedback data, a number of different voltage and/or current levelswithin the transmitter may be monitored, for a myriad of purposes,including but not limited to:

1. [Transmitter] Prior to laser diode—voltage and current

2. [Receiver] Downstream of the photodiode assembly—voltage and current

3. [Receiver] Downstream of the DC/DC converter—voltage only

4. [Transmitter] Downstream of the FSOC photodiode—voltage only

These measurements may produce all the information needed to makedecisions about safety of the system in any situation. The receiver isconstantly updating its state to the transmitter. Interruption of thatstate update or mismatch to ideal parameters for power reception resultin a decrease in high power laser beam power. The beam cut off timingrequirements for the system may be dependent on the output power andbeam spot of the laser diode. It is therefore possible to assign cut-offtimes dynamically between the transmitter and receiver if necessary.

In its full implementation, the present disclosure may offer faultdetection and, in some instances, fault tolerance. For all criticalsafety features, there may be one or more fault tolerances built intothe hardware and software. The safety critical hardware may be solelycontained on the transmitter side of the system as the hazardouscondition is only created by the transmitter, namely the high-powerlaser beam. This critical hardware may include the optoelectronicsensor, the operational amplifier, the processors implementable invarious forms, and the laser diode power supply.

Some fault tolerance conditions may include:

1. A single fault, whether through an electrical short or open circuitof the optoelectronic sensor. Such a fault would cause a voltage outputof zero, in the short case or float, in the open circuit case. In etherfault condition, the processor would recognize a repeated bit sequenceover several clock cycles that would automatically trigger beam shutdown.

2. A single fault to either the processor or the laser power supplyresulting in an electrical short or open circuit. In the open circuitcase, there would be no current feeding the power supply circuit andthus there would be no possible mechanism for energizing the laserdiode. In the short circuit case, the processors would have thecapability of running a check of the aforementioned monitored laserdiode current against the trigger state of the processors to lasersupply switch. The current reading would be interpreted as a 1 or 0representing current present in the circuit or absent, respectively.That binary output may be compared against the trigger state of theprocessor via an OR operation. This comparison may output a signal tocease supply to the laser diode in an unsafe circumstance.

3. An additional software check on the fault state that requiresmultiple assigned and expected signals to be present before initiatingthe high-power supply for the laser. Any absence or off-nominal valuesof these specific signals would result in the laser diode remaining off

In one embodiment, the safety optoelectronic components may be designedspecifically for detection in the IR wavelengths, but distinct from thehigh-power laser wavelength. The use of photodiode/LED pairs matched tothe same operational wavelength allows for communication over nearly180-degree full angle field of view (FOV) without the need of additionalfocusing or conditioning optics.

The method of operation and implementation of the safety systemdescribed herein equally allows for communication of system state datato any remote processor determinable via a User Interface (UI), whichmay be further used to fix potential connection issues by manuallyremoving an obstacle or interruption. In this embodiment, a lack ofsignal for a specific bit count (time period) may lead to a UI messagebeing sent informing the user of the current fault. The message type isinterpreted from the data received from the low power laser beam, FSOClink. Although greatly simplified for the use of a FSO signal, theinternal electrical modulation or messaging can be far more complexwithout taxing the processor. This may improve the uptime, overallfunctional efficiency and usability of the system.

Turning now to the receiver, which is first illustrated in FIG. 3 aspart of a receiver or host structure, i.e., the device in which thereceiver 60 is installed, the receiver 60 is comprised of a photodiodeassembly 62 including a photodiode array 63. The photodiode array 63, ordiode, is not limited to diode-based technology and may be implementedwith alternative technologies, now existing or developed in the future,capable of performing similarly. Nor is the photodiode assembly 62limited to wireless power transfer embodiments. The photodiode assemblyof the current disclosure may be readily adapted to a variety of otherembodiments where the efficient transfer of light into current andvoltage is desired, in applications requiring precise alignment, inapplications involving optical signals in extreme environments, orsimilar embodiments.

In an embodiment, the photodiode assembly 63 may be capable of highoptical to electrical power transduction and associated powerelectronics that are responsible for receiving the electrical power inthe form of current and voltage and appropriately converting the voltagevia an electrical voltage converter 64, such as a boost converter, thatvoltage and current into a usable voltage and current for batterycharging, a battery charger manager 66 for controlling the flow ofcurrent and bias voltage applied to the rechargeable storage device orbattery 68, and a low power processor/controller 70. The processorcontroller may sample voltage and current outputs from both thephotodiode assembly 62 and battery charge manager 66, encode andmodulate/demodulate digital and analog signals to and from a remotetransmitter unit, push user information from local buffers totransmitted RF connections (which may be in the form of Bluetooth, WiFior similar), and monitor the temperature of the photodiode assembly'sheat sink via a temperature sensor 72 and communicate that state to aremote transmitter via antenna 73 or low power laser beam.

In order to increase the usability of systems deployed in what may bechaotic and unpredictable user environments, one or more visual UIindicators, such as RGB status LED 75, may be added. In an embodiment,the primary UI 75 displays a visual indicator with different or similarstates, but not identical states. Each of the states represents, in asimple sense, the overall state of either the receiver, the transmitter,or both. The plurality of state representations through such visualindicators will allow the user to interact more efficiently with thesystem. In an embodiment, a small circle with a dot in the middlerepresents the visual indicator and one state. A small circle with thedot blinking represents a second state. A circle without the dotrepresents a third state. A circle blinking represents a fourth state.Different colors may be used for the circle and dot in differentcombinations to represent additional states. In these aforementionedchaotic environments, the visual indicator will provide cues for userknowledge. In one such implementation, a second state may mean there ispartial or full block in the LOS between the transmitter and receiverand thus action should be taken to correct this state, such as move thedevice or move the obstruction. A first state may represent that thedevice is engaged in wireless power transfer, a third state mayrepresent the transmitter is trying to find the receiver, and a fourthstate may indicate that the transmitter and receiver are not synced.

Further receiver 60 elements include: heat sink/spreader elements 74that may control thermal properties of the photodiode assembly whensubjected to the high power laser beam; an IR communication photodiode76 collocated with the photodiode assembly 63; an IR LED 78 collocatedwith the photodiode assembly 63, a compound parabolic concentrator (CPC)mirror element 80; an antireflective (AR) coated, scratch resistantwindow surface (not shown) at the collector inlet over the mirrorelement 80; a Li Ion or Li Polymer battery housing (not shown) formodular attachment of the battery 68 or the incorporation of a receiverrechargeable unit; and a device enclosure (not shown) to package and/orcontain the above elements. In an embodiment, the receiver devices maybe integrated into a larger device used in the consumer electronics,medical, or industrial industries.

The photodiode assembly 63 may capture and convert a high-power opticalbeam into electrical power in the form of current and voltage. The powerelectronics may use the output voltage and current from the photodiodeassembly and convert it through the voltage converter 64 to a voltageapplicable for battery charging, depending on the battery orrechargeable load impedance. In some embodiments, the voltage converter64 may not be necessary as the raw output of the photodiode assembly 63may fit within the operational voltage and current of the connectedenergy storage device 65. The power electronics may also track the inputimpedance of the photodiode assembly 63 and control the voltage andcurrent based on this device impedance in the form of Maximum PowerPoint Tracking (MPPT). The battery charger manager 66 circuit may beresponsible for controlling current and voltage into the rechargeablestorage device 68 based on optimal charge cycle per rechargeable storagedevice configuration. Current and/or voltage output by the batterycharge manager 66 may be measured by current/voltage measurement 67 Theoutput from the photodiode assembly may also be used to temporarilypower other active elements of the receiver system.

The processor or controller 70, such as an ARM Cortex or similarprocessor, may collect data from the photodiode assembly 63 and thevoltage converter 64 output voltage information and encode thatinformation, via encoder/decoder 77, onto a carrier wave via modulationprocesses through an IR transmitter 82. The voltage feedback informationmay provide interpretation of transmitter beam landing accuracy and anyemergency or hazard detection signals. The processor 70 may also beresponsible for demodulation of any transmitter-generated signals thatare received, decoding that information, and processing and performingany suggested action resulting from that information. The processor 70may further store information in a local buffer (not shown) forsubsequent push to a Bluetooth, WiFi, or other RF connection, such asinformation and statistics on system efficiency and system health forforwarding to remote storage locations based on the required timing forneeded specific information.

IR photodiode 76 converts an incoming IR low power laser beam signalinto electrical pulses that are amplified and sent to the processors orcontroller 70. The IR LED 78 converts electrical pulses to opticalsignals for transmission outside of the receiver's mechanical structurein a wide FOV. Optomechanical enclosures (not shown), such as windowelements in connection with the inlet of the CPC device 80 and over thephotodiode assembly 62 may seal off sensitive optoelectronic surfaces,ensure a continuous outer mold line (OML) of the receiver/structure, andensure favorable optical paths for incoming and outgoing light.

As further illustrated by the lens stage of FIG. 13, the window used toseal off the inlet may also have dispersive properties near theoutermost surface, to prevent back-reflections internal to the CPC 80from being focused in the external environment, and focusing propertiesnear the innermost surface, to aid in light collection at the outlet.Such properties can be achieved with an arrangement of Fresnel lenses600, as further illustrated by FIG. 12, that will focus incoming lightto the photodiode assembly 602 and diffuse radiation reflected withinthe CPC 80 and not captured by the photodiode assembly. Morespecifically, the Fresnel lens or other lens 600 may have a positivefocal length for concentrating incident radiation at the inlet to theaperture on the outlet and the photodiode assembly 602. At the sametime, the inner most surface of the Fresnel lens(es) may have a negativefocal length for diffusing reflected radiation within the CPC 80 out tothe CPC 80 over a larger area. Divergence of light out of the receiverinlet will further increase the laser safety of the entire system as theoutgoing light has far larger irradiance. As shown in FIG. 13, the oneor more Fresnel lenses 600 may be sandwiched between two primer layers602 and 604, two thermally cured dip coats 606 and 608, two hardanti-reflective stacks 610 and 612, which the outside surface coatedwith a super oleophobic/hydrophobic top coat 614.

As will be further described below with reference to FIG. 4A and FIG.4B, a CPC mirror 80 may be employed and sized to the enclosure in whichthe receiver 60 is located. The CPC mirror 80 may be used for pure lightcollection, to increase FOV light capture for the receiver 10, and forimproved uniform illumination of the photodiode assembly 63. Internalsurfaces of the mirror 80 may be coated with a thin layer of depositedmetal in order to preserve, to the fullest extent possible, beam power.In an embodiment illustrated in FIG. 4B, the CPC mirror 80 may betruncated or extended at a shallow angle 81 toward the inlet in order tofurther increase the FOV of the system. The shallow angle or chamferedsurface may also be extend 360 degrees around the CPC or less givenpreference of the application. A modular battery housing (not shown) mayalso be employed that includes a mechanical structure for housing acompact energy storage device 68 that could include but is not limitedto a Li Ion or LiPo battery cell(s) or a bank of capacitors orsupercapacitors, configurable and electrically connected to the fullreceiver device.

The receiver may be comprised of two major subsystems: the power receivesubsystem and communication subsystem. Subsystem functionality may bedesigned to be modular with minimal interface requirements between them.The intent of a modular system design is to allow for a power onlyimplementation or a communication only implementation, or both. In amodular design, interfaces (i.e., subsystem IO) that perform functionaltasks based on input from the other may be reprogrammed to another hostsystem or left open. The technical implication of this is the ability toincorporate just an FSOC subsystem or just a power receive chain into aplurality of upstream systems.

The receiver components may be designed with simplicity and a small formfactor in mind. Incorporation of the receiver into consumer electronicapplications may set the requirements for size, power usage, and powerdensity, which can later be developed into a standard for such devices.The electrical circuitry may be kept as simple as possible in order todecrease board/device space and power consumption. The voltage converter64 may play a role in decreasing device size. The boost converter 64 maybe responsible for increasing the transducers output voltage to anappropriate battery charging voltage. Every converter stage may alsorequire the use of power (as these are active switching components),which may serve to reduce the overall efficiency of the receiver 10. Inorder to decrease the efficiency loss to less than 8 percent at thisstage, the boost converter 64 may use Maximum Multiple Power PointTracking (MPPT), which is similarly implemented in solar cell systems,but which is not known to be used in IR laser-based systems, within thefirst converter stage. The MPPT architecture is a “test and adjust” typeprobing the required input impedance in order to maximize the powerdelivered from the photodiode assembly by ensuring matching circuit anddevice impedances.

An additional battery charger manager 66 may be employed to ensure thefull charge cycle for a Lithium Ion, Lithium Polymer, or other batterychemistry is accommodated. If the battery or storage device of the hostreceiver is not Lithium based, the battery charger manager may beunnecessary. A bulk/storage capacitor 84 may also be used between thephotodiode assembly 62 and the voltage converter 64 in order to providethe voltage converter 64 with filtered electrical power.

The design of the receiver 60 may also seek to keep leads as short aspossible to minimize lead resistance and distributed inductance, i.e.,for transient charging cycles. The voltage output of the photodiodeassembly, an embodiment of an optical to electrical converter, may besampled by the processor 70 and may be considered part of the safetysubsystem. Sampled data may be stored and forwarded to encoder/decoder77 to encode a bit sequence on a predefined carrier frequency to betransmitted by the FSOC LED 78. One uniqueness of this architecture isthat the receiver 60 sends simple bit streams to the transmitter 10,messages that require close to no message overhead. The processor of thetransmitter 10 performs the heavy lifting in terms of interpreting thebit sequence.

Finally, the core logic on the receiver 60 may come from the processor70. The processor 70 may interpret feedback from the IR transceiver 82and encoder/decoder 77. The receiver 60 may also incorporate acommunication system that is an improvement to the IrDA (Infrared DataAssociation) standard. As the IrDA standard is designed for operationbetween 1 cm and 1 meter, a greater range is needed to make the presentdisclosed technology more useful and distinctive. At the same time,ambient light sources may contaminate the sensor causing interference tosmall optical input signals. In order to overcome this issue in anembodiment, it may be desirable to increase the magnification of the IRFSOC light with a hemispherical lens on the photodiode receiver 76 anddesign a narrow bandpass filter on the photodiode receiver back end. Thebandpass filter may only allow a certain band of wavelengths throughwhile suppressing both DC ambient and sporadic external sources. Furtherdistance increase may be gained from driving the FSOC LED at its maximumsupply level while maintaining eye safety limits.

The optical architecture of the receiver 60 may be primarily comprisedof a scratch resistant hydrophobic, and possibly oleophobic,antireflective (AR) coated optical window 90 as illustrated in FIG. 4A,FIG. 4B and FIG. 13 that interfaces with the receiver into which thereceiver 60 is incorporated, known as a lens stack. The external opticalinterface with the receiver and ambient environment may be flush suchthat scratches or breakage that may occur with an off-set or raisedsurface (or domed surface) are avoided. The window itself may be ARcoated exhibiting scratch resistance and hydrophobicity/oleophobicity.This may maintain a clean IR transmissive surface at the inlet of theCPC to ensure fidelity of the beam path to the receiver photodiodeassembly while avoiding dirt, moisture and grime accumulation on theoptical surface.

As previously noted, and further illustrated in FIG. 4A and FIG. 4B, aCPC mirror 80 may focus incoming light at its inlet onto the photodiodeassembly 63 at its outlet. The optical to electrical converter may becoupled with the FSOC LED 78 and IR photodiode 76 of FIG. 3. The CPCmirror 80 may be uniquely shaped as a light collector and may materiallyincrease the FOV of the overall system. One advantage of the CPC mirroris that it eliminates the need for a collecting lens to focus light onthe photodiode. The internal walls of the CPC may be coated with 100-300nm of silver or gold or aluminum depending on the embodiment with anenvironmental protection layer to increase part life. The point behindthe coating may be to ensure maximum reflectance across the IR beamingwavelength range. Loss due to reflection or absorption at this interfacemay be <1%. The overall shape of the CPC mirror 80 may be based on theintersection of two parabolas and thus may have a cone or bowl likeappearance. As shown in FIG. 4B, the CPC may be further truncated on theinlet side of the mirror in order to allow for tapering the edges 81with connection to the OML or for allowing an increased system FOV.

The photodiode assembly 63 may be integrated into the base of the CPCmirror 80 to ensure maximum exposure to incident light. As noted, a NIRAR coating may be applied to the top window surface 90 flush with theexternal surface of the device. In order to withstand the stochasticuser environment, there may be a need to maintain a hard coat on the topsurface to decrease the probability of scratches that could degrade thesurface and therefore the overall effectiveness of the system. Inaddition, fingerprints and other environmental contaminants are likelyto be present during the lifetime of the part. The hydrophobic surfacemay help to ensure minimal surface contamination. The hydrophobicitylayer may be implementable during production and during use throughtemporary and permanent coatings. A similar integration may be used foroleophobic coatings. Thus, users may “touch up” optical surfaces ifdesired, which may lead to increased performance. The IR LED 78 and IRPD 76 form the basis of the communication and safety subsystem of thereceiver 60. As previously noted, the FSOC low power laser beamco-propagates with the high-power beam to form a virtual enclosurearound the high-power beam. The FOV of the low power laser beamcomponents may therefore need to be greater than or equal to the FOV ofthe high-power laser beam components in order to ensure that thehigh-power laser beam will remain contained within the light cone ofFSOC low power laser beam and communication link with the transmitter 10at all possible power beaming positions. In various embodiments, eitheractive or passive lens or optical material may be added to the beam pathof the low power laser beam in order to further converge or diverge theFSOC beam and ensure such coverage with respect to the power beam. TheFSOC optoelectronic components may be located as close as possible tothe power receiving photodiode assembly. These embodiments may includeapplications where there are further transmission range requirements.

The overall physical size of the integrated receiver may be designed tobe compatible with the environment in which the receiver is used. Formany mobile consumer electronics applications, this means the dimensionsper side are in the 10 mm or less range. However, these dimensions aremerely exemplary and the present disclosure is not limited to suchdimensions. Nevertheless, maintaining a small volume may allow thetechnology to be integrated into a variety of hardware devices. Theoverall supporting structure (not shown) for the CPC mirror 80 may becentered on stabilizing the CPC/photodiode assembly. The CPC itself maybe manufactured individually or cut from a cube made of opticalmaterial. Integration of the CPC with the photodiode may happen inconjunction with integration into the receiver or before.

Moving now to the photodiode assembly 63 of the receiver, reference ismade to FIG. 5-FIG. 11. The photodiode assembly 63, may be aback-contact photodiode assembly designed specifically for high powerlaser optical to electrical transduction. As will be further describedbelow with references to FIG. 9A and FIG. 9B, the back-contactphotodiode assembly may be comprised of a plurality of photosensitiveregions arranged in pie wedges to maximize photon exposure and decreasethe component footprint, as well as to achieve uniform response fromeach photodiode in a pie wedge. The device band structure may bespecifically designed to optimize a narrow wavelength absorption bymanipulation of the composition of the In_(x)Ga_(1-x)As semiconductormaterial from which it may be formed. Namely, “x” is carefully chosen sothat light may be efficiently (>95%) absorbed within 2˜5 μm thickness,while the bandgap may be only slightly smaller than the photon energy tomaximize the power conversion efficiency. The back-contacts, which mayserve as both electrical and thermal pathways, may be sized for minimalseries resistance, sufficient heat capacity, have a large surface areafor heat dissipation, and for mass manufacturing. Each of these aspectsare further described in detail below.

As illustrated in FIG. 5, the top substrate surface 100, i.e., thesurface upon which light is incident, may be an uninterrupted bulk,lightly doped InP substrate. In this context, lightly doped meansconcentrations of <10{circumflex over ( )}16 atoms/cm{circumflex over( )}3 of impurities. In order to prevent incoming radiation fromreflecting off the surface of the InP, the top substrate layer 100 maybe coated with a thin anti reflection layer 102 with a thickness thatmatches a quarter wavelength of the intended incoming radiation. Theanti-reflection (AR) layer 102 may be Si3N4 or another compound with arefractive index close to the square root of product of the refractiveindices: n_(air)×n_(semiconductor). The substrate 100 and underlyinglayer(s) may be sized based on the absorption coefficient of 1400-1600nm light in InP/InGaAs material. The penetration depth of light as afunction of wavelength is further illustrated in FIG. 6. As illustratedby the plot, within the active InGaAs region 200 most of the light iscompletely absorbed within a few microns.

An additional consideration for the active region of the photodiodeassembly 63 is the size of the depletion width, or the area in whichphotogenerated electrons and holes are diffused to n+ and p+ regions dueto the electric field setup within this region. Inside this activeregion, the electric field may be very strong, such that electrons areseparated to create the electron hole pairs. The corresponding energyrequired for the separation is known as the band gap energy. The bandgap energy combined with knowledge of the wavelength of incident lightmay allow for optimization of the material atomic concentrations.Between the substrate layer 100 and the InGaAs layer 104 is aheterojunction buffer layer 106 that may prevent electrons and holesleaking back into the InP substrate layer 100, as further illustrated inFIG. 7. In other words, the heterojunction buffer 106 may implementunidirectional (only to the bottom n+/p+ electrode regions 108, not thetop InP layer) photo carrier collection. This may be an ideal situationfor producing efficient optical to electrical energy conversion.

As further illustrated in FIG. 8, electron hole pairs are generatedwithin the active n+/p+ electrode regions 108 as a function of incidentlight. A PIN structure may therefore be formed via alternating n+/p+electrode regions 108 with a small width between them and the electroderegions 108. The small separation distance may ensure liberatedelectrons 114 within the active region, are swept toward n+ regions andholes 116 within the active region are swept toward the p+ region,creating a steady stream of current. The n+ and p+ electrode regions 108may be configured such that there is a conductive path to theinterdigitated back-contacts 110. A thin passivation layer 112 betweenthe back-contacts may prevent electrode regions from directly shorting.The passivation layer 112 may be made from a plurality of suitablematerials (Cu, Al, Ag, etc.).

As previously noted, the back-contacts, each in the form of afinger-like structure, are interdigitated based on the spacing betweenthe p+/n+ electrode regions 108. This may enhance collection efficiencyby having a distributed periodic structure equally spaced on thebackside of the photodiode assembly 63. The back-contacts may be finestructures formed into pie shaped sections in order to decrease seriesresistance. In one embodiment illustrated in FIG. 9A, the interdigitatedfingers 210 and 212 are substantially straight. In a second embodimentillustrated in FIG. 9B, the interdigitated fingers 210 and 212 may beshaped to conform to the radius of curvature of the overall device. Forexample, as shown in FIG. 9B, each pie shaped section 250 has smaller,slightly curved interdigitated fingers towards a central area 252 andsubstantially longer interdigitated fingers towards an outer area 254 soas to conform the circular shape of the photodiode assembly 63. Byshaping the p+/n+ regions, which are adjacent to the back-contactelectrodes, to conform to the circular shape of the photodiode assembly63 it may be possible to improve overall collection efficiency and powerconversion efficiency.

The anode 200 is serially connected to the cathode 202 ccw(counter-clock wise) around the photodiode assembly 63. The serialconnection may allow for threshold voltages generated by each of theindividual sections to be additive, thereby producing an aggregatevoltage at the device terminals. The sections of the assembly mayadditionally be monitored, as illustrated by monitoring points 400 ofFIG. 11, and measured for output voltage so as to determine the relativeillumination intensity of each section. This voltage information may becommunicated to the transmitter to help refine beam pointing. The finefinger structures are positioned just below the p+/n+ electrode regions108 where maximum collection of photogenerated electrons within theactive region can occur. The interdigitated design may allow for fineplacement of the electrode region fingers to setup a continuous fieldstructure across the n+/p+ electrode regions 108. Finger length isminimized to decrease series resistance and periodic electrode railsprovide low resistance connection from section to section. To preventshorting of the fine finger structure, gap filling with a siliconepolymer, h-BN, or similar electrically resistive material, the backsurface may provide sufficient isolation 206. It should be noted thatthe top InP surface 100 does not need to be etched or separated intodiscrete sections like the back-contact pattern, as the presentdisclosure need not rely on the optoelectronic performance of the bulksubstrate 100.

The photodiode assembly 63 of the present disclosure may be integratedin various forms. One such method, as further illustrated in FIG. 10,involves integration onto a PCB (printed circuit board) in which theanode and cathode are routed out of the device as traces. In thisembodiment, the device may be used in a variety of forms, e.g., areceiver element used in a laser based wireless power transmissionsystem providing power to co-located devices, a sensor used forapplications involving high powered lasers, and as a fine tune oralignment sensor, when wired individually, based on individual sectionfeedback or in a plurality of other optical based systems. Furtherintegration into complex or standalone systems may also be possiblebased on the application.

In FIG. 10 and FIG. 11, the InGaAs assembly/chip 300 may be bonded to asmall section of copper film 302. The bond area may cover the entireback of the photodiode assembly/chip 300 and as such a smallelectrically isolating layer (not shown) may applied between the copperfilm and the back-electrode contacts. The copper film 302 may bonded bya heat conduction epoxy layer 304 onto a heat sink 306 and/or a blankcopper pour 308 (the thickness of which may vary) on the PCB. The anodeelectrode may exit the side of the chip and be attached either directlyto the PCB via traces or wiring. The disclosed device may thereforemaintain a compact form factor for increased modularity and ease ofcomponent integration via electrode pads. The disclosed device may alsoallow for wiring in parallel depending on the requirements of the loadand the expectation of inputs to downstream circuitry.

The overall operation of the power transfer device may be described asfollows. The receiver may recognize its State of Charge (“SOC”), orsource voltage, or a plurality of other indicators, are lower than apredefined threshold and ping, or wake up, the embedded wireless powertransfer hardware. An IR LED on the front face of the receiver may thenbegin emitting light periodically as a “beacon signal” to any nearbytransmitter. The beacon signal may be a FSOC signal comprised of a shortdigital data stream modulated on top of a carrier signal containing adevice unique ID (device name, make, revision, type, etc.), a state ofcharge (SOC) indication, and information for the transmitter to generatethe lock ID. The lock ID is generated within the transmitter as aposition-based record (in coordinates relative to the beam steeringsubassembly) of the last known location of the receiver as confirmed bythe receiver over the FSOC link. In another embodiment, the receiver mayuse a built in RF antenna to communicate state information to a nearbytransmitter. The transmitter may use a built in RF antenna to checkreceiver SOC, battery voltage or the like and to determine ability ofthe receiver to participate in wireless power beaming processes. In anembodiment, the transmitter may choose not to engage the receiver in thewireless power beaming process if transmitter determines that thereceiver's remaining battery charge is too low for it to be beneficial.The transmitter may also decide against engagement with a specificreceiver if the device priorities have been set in such a mannerthat: 1) other, more critical, units require power beyond what thetransmitter is able to provide to the requesting device; 2) thetransmitted device ID is determined to not be serviceable by thetargeted transmitter (e.g., the device firmware or hardware is out ofdate or unlicensed); or 3) there is a recognized error state set in thereceiver. The transmitter may then release the connection to thereceiver, such that other receiver functions can take priority.

Meanwhile, the transmitter may monitor its IR photodiode for a beaconsignal and processes the receiver digital information once itsphotodiode is activated by the beacon signal. As the beacon signal isdetected, the transmitter IR camera may switch from an “idle” state toan “active” state and begins to localize the IR beacon from thereceiver. The IR camera may change state, i.e., from active to idle,only after a predetermined “no detect” period has passed, which may beapproximately 30 seconds (the time period, i.e., more or less time, doesnot change the method of this embodiment) after the transmitter's IRphotodiode last detected a signal.

After the transmitter IR camera has identified the approximate locationof the beacon signal, a continuous communication link via FSOC may beestablished. The transmitter IR low power laser diode may begin toexecute a localized scan pattern in the vicinity of the approximatelocation of the identified receiver. Once that scan is caught by thereceiver photodiode, the communication link/handshake may beestablished. The predetermined period for establishing the link may becalled the “handshake event time”. As described above, the low-powertransmitter IR beam is coincident with the high-power beam of thetransmitter. The transmitter's low power laser beam produces a largerspot size at the receiver's beacon photodiode than does thetransmitter's high-power beam at the receiver's power beamingphotodiode.

Once the handshake event has occurred, the transmitter high power laserbeam, in a low power setting, may then sweep across the area localizedby the transmitter's low-power laser diode in order to locate the powerbeaming photodiode of the receiver. The low power laser diode may modifythe output spot based on state. This includes through electricallyactivated optics, which may be a liquid lens. The receiver LED mayreport back power data to the transmitter in microsecond intervals overthe established communication channel. Once the transmitter IR powerbeam has swept back across the local maxima, as reported by the receiverIR LED, localization may be considered completed and the high-power beamsupply may be increased to suit the type of device. The low-power laserbeam may maintain continuous communication with the transmitterphotodiode to deliver information on transfer efficiency, receivedpower, SOC, and current and voltage readings from the power photodiode.

Any loss of reported information lasting longer than the predeterminedsafety shut off time may cause an internally generated hazard-warningsignal to the transmitter laser driver to decrease the beam power tosafe levels. Any end of beam activities may be directly signaled by thereceiver IR LED (either through lack of data or specific bit sequences)and interpreted by the transmitter IR photodiode. The duration of anyend of beam activities signal may not last more than the predeterminedsafety shutoff time.

In the event of an end of beam activity, for example, if the link marginefficiency or voltage/current statistics from the receiver powerphotodiode assembly is violated, the transmitter may attempt tore-localize the receiver power photodiode, starting with the last knownlocation of the receiver, the aforementioned lock ID which is stored bythe transmitter in case tracking is required. The same transmitter scanpattern described above may be engaged with the receiver IR LEDreporting back incident power.

If either the transmitter or the receiver electronics determine aninternal condition (vs. an external LOS interruption) that would inhibitnominal operation, the transmitter/receiver will communicate that to thereceiver/transmitter and enter a fail-safe mode. No furthercommunication or power transfer may occur until the fault is cleared.Faults will be classified per category: internally resettable,externally resettable, User Equipment, “UE”, replacement, etc. Anindication of either the transmitter or the receiver being in afail-safe mode may be indicated visually with a blinking LED on thetransmitter and an error message on the UE. While the presentlydescribed operational methods are described in the context of theparticularly disclosed power transfer system set forth herein, theoperation methods are not limited to just the described device and couldbe implemented with different types of power transfer devices inaccordance with the present disclosure.

In an embodiment, an assembly for optical to electrical power conversioncomprises a photodiode assembly. The photodiode assembly comprises asubstrate layer having a light exposed side and an internal side; anantireflective layer adjacent the light exposed side and configured toprevent incoming light from reflecting off of a surface of the lightexposed side; a heterojunction buffer layer positioned adjacent theinternal side; an active area positioned adjacent the heterojunctionbuffer layer and configured to convert photons from the incoming lightinto liberated electron hole pairs, wherein the heterojunction buffer isconfigured to prevent electrons and holes of the liberated electron holepairs from moving toward the substrate layer; and a plurality of n+electrode regions and p+ electrode regions positioned adjacent theactive area and configured in an alternating pattern with gaps betweeneach n+ electrode region and each p+ electrode region and furtherconfigured to receive and generate electrical current from migration ofthe electrons and the holes, to provide electrical pathways for theelectrical current and to provide thermal pathways, the alternatingpattern including a series of pie shaped sections, each pie shapedsection having a narrow end adjacent a central area of the n+ electroderegions and the p+ electrode regions, each pie shaped section formed ofinterleaved rows of the n+ electrode regions and rows of the p+electrode regions; an anode back-contact configured to align with aportion of the alternating pattern corresponding to the rows of the n+electrode regions; and a cathode back-contact configured to align with aportion of the alternating pattern corresponding to the rows of the p+electrode regions.

In the embodiment, the active area is a lightly doped InGaAs layer. Inthe embodiment, the photodiode has a circular shape, and wherein each ofthe interleaved rows of the n+ electrode regions and rows of the p+electrode regions are curved and configured to conform to the circularshape of the photodiode.

In the embodiment, further comprising a thin film thermal dissipativematerial placed in contact with a non-illuminated side of the photodiodeand configured to conduct heat away from the photodiode during highintensity light exposure and to reduce potential for an electricalshort. In the embodiment, the film thermal dissipative material is anelectrical insulator.

In the embodiment, the substrate layer has an etch pitch densityconfigured to avoid scattering of the incoming light.

In the embodiment, the photodiode is formed from one or more of alithography method, a crystal growth method, and an ion implantationmethod.

In the embodiment, the heterojunction buffer layer includes anon-uniform concentration of materials throughout and is configured toform a better lattice matched structure.

In the embodiment, the photodiode is an optical to electrical converterconfigured to be integrated into a compact device. In the embodiment,the photodiode is mounted to a heat sink or heat spreader within thecompact device.

In the embodiment, the electrical current is measurable at one or moreof the anode back-contact and the cathode back-contact of each pieshaped section. In the embodiment, the measured electrical current ofeach pie shaped section corresponds to a relative illumination intensityfrom incoming light on each pie shaped section. In the embodiment, themeasured electrical current of each pie shaped section is communicatedto a source of the incoming light to refine a direction of the incominglight.

In the embodiment, the electrical current is configured to provide powerto an energy storage device or other active components.

Having thus described the different embodiments of a wireless powertransfer system and methods of operating the same, it should be apparentto those skilled in the art that certain advantages of the describedmethods and apparatuses have been achieved. In particular, it should beappreciated by those skilled in the art that the assembly for convertingoptical light to electrical power may be implemented using differenttypes of hardware and in different combinations than described hereinand operated in a variety of different manners than that described. Itshould also be appreciated that various modifications, adaptations, andalternative embodiments thereof may be made within the scope and spiritof the present disclosure.

What is claimed:
 1. An assembly for optical to electrical powerconversion, comprising: a photodiode assembly; comprising: a substratelayer having a light exposed side and an internal side; anantireflective layer adjacent the light exposed side and configured toprevent incoming light from reflecting off of a surface of the lightexposed side; a heterojunction buffer layer positioned adjacent theinternal side; an active area positioned adjacent the heterojunctionbuffer layer and configured to convert photons from the incoming lightinto liberated electron hole pairs, wherein the heterojunction bufferlayer is configured to prevent electrons and holes of the liberatedelectron hole pairs from moving toward the substrate layer; and aplurality of n+ electrode regions and p+ electrode regions positionedadjacent the active area and configured in an alternating pattern withgaps between each n+ electrode region and each p+ electrode region andfurther configured to receive and generate electrical current frommigration of the electrons and the holes, to provide electrical pathwaysfor the electrical current and to provide thermal pathways, thealternating pattern including a series of pie shaped sections, each pieshaped section having a narrow end adjacent a central area of the n+electrode regions and the p+ electrode regions, each pie shaped sectionformed of interleaved rows of the n+ electrode regions and rows of thep+ electrode regions; an anode back-contact configured to align with aportion of the alternating pattern corresponding to the rows of the n+electrode regions; and a cathode back-contact configured to align with aportion of the alternating pattern corresponding to the rows of the p+electrode regions.
 2. The assembly as recited in claim 1, wherein theactive area is a lightly doped InGaAs layer.
 3. The assembly as recitedin claim 1, wherein the photodiode has a circular shape, and whereineach of the interleaved rows of the n+ electrode regions and rows of thep+ electrode regions are curved and configured to conform to thecircular shape of the photodiode.
 4. The assembly as recited in claim 1,further comprising a thin film thermal dissipative material placed incontact with a non-illuminated side of the photodiode and configured toconduct heat away from the photodiode during high intensity lightexposure and to reduce potential for an electrical short.
 5. Theassembly as recited in claim 4, wherein the film thermal dissipativematerial is an electrical insulator.
 6. The assembly as recited in claim1, wherein the substrate layer has an etch pitch density configured toavoid scattering of the incoming light.
 7. The assembly as recited inclaim 1, wherein the photodiode is formed from one or more of alithography method, a crystal growth method, and an ion implantationmethod.
 8. The assembly as recited in claim 1, wherein theheterojunction buffer layer includes a non-uniform concentration ofmaterials throughout and is configured to form a better lattice matchedstructure.
 9. The assembly as recited in claim 1, wherein the photodiodeis an optical to electrical converter configured to be integrated into acompact device.
 10. The assembly as recited in claim 9, wherein thephotodiode is mounted to a heat sink or heat spreader within the compactdevice.
 11. The assembly as recited in claim 1, wherein the electricalcurrent is measurable at one or more of the anode back-contact and thecathode back-contact of each pie shaped section.
 12. The assembly asrecited in claim 11, wherein the measured electrical current of each pieshaped section corresponds to a relative illumination intensity fromincoming light on each pie shaped section.
 13. The assembly as recitedin claim 12, wherein the measured electrical current of each pie shapedsection is communicated to a source of the incoming light to refine adirection of the incoming light.
 14. The assembly as recited in claim 1,wherein the electrical current is configured to provide power to anenergy storage device or other active components.